Modern Synthesis dead?

There seems to be new interest in the blogosphere regarding what Stephen Jay Gould had to say about evolution, invigorated, at least in part, by Jerry Coyne’s post on The Loom. This appears to have grown into the creation of a “ScienceBlogs Book Club” which will discuss Gould’s massive book, The Structure of Evolutionary Theory. I read it when it came out. I am certain that Larry Moran has read it. But we’re not on ScienceBlogs (he declined, and I was never approached). I also am fairly sure that PZ Myers has read it, so maybe he can provide some perspective.

My last post dealt briefly with one aspect of this discussion, namely a misinterpretation of punctuated equilibria as representing a saltatationist mechanism. In no small part, this has been based on cherry picking quotes from Gould’s diverse writings, which did indeed cover mutations of substantial effect in addition to patterns of speciation in geological timescales.

This time I want to revisit one of Gould’s most famous quotes, and certainly his most infamous. The version that is most familiar, I believe, is the one cited in Charlesworth et al. (1982), who quote Gould thus:

I have been watching it [neo-Darwinism] slowly unravel as a universal description of evolution … I have been reluctant to admit it … but … that theory, as a general proposition, is effectively dead, despite its persistence as a text-book orthodoxy.

Strong claims, to be sure. But evolutionary biologists, I should hope, are always wary of ellipses, and that passage has several.

Here is Gould’s (1980) quote in full (emphasis added):

I well remember how the synthetic theory beguiled me with its unifying power when I was a graduate student in the mid-1960’s. Since then I have been watching it slowly unravel as a universal description of evolution. The molecular assault came first, followed quickly by renewed attention to unorthodox theories of speciation and by challenges at the level of macroevolution itself. I have been reluctant to admit it — since beguiling is often forever — but if Mayr’s characterization of the synthetic theory is accurate, then that theory, as a general proposition, is effectively dead, despite its persistence as textbook orthodoxy.

The question is, what was Mayr’s characterization that Gould considered effectively dead as a general proposition?

Ernst Mayr (1963) (emphasis added):

The proponents of the synthetic theory maintain that all evolution is due to the accumulation of small genetic changes, guided by natural selection, and that transspecific evolution is nothing but an extrapolation and magnification of the events that take place within populations and species.

Polyploidy. Genetic drift. Mass extinction. Gould said many controversial things, but his claim, without ellipses, that the modern synthesis so defined had perished was pretty neutral.

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References

Charlesworth, B., R. Lande, and M. Slatkin. 1982. A neo-Darwinian commentary on macroevolution. Evolution 36: 474-498.

Gould, S.J. 1980. Is a new and general theory of evolution emerging? Paleobiology 6: 119-130.

Mayr, E. 1963. Animal Species and Evolution. Harvard University Press, Cambridge, MA.



14 comments to Modern Synthesis dead?

  • Jonathan Badger

    I’m not generally a big fan of Mayr or arch-selectionists in general, but I don’t think that his writing (as per your emphasis) “guided by natural selection” is the same thing as claiming that natural selection is the *only* force affecting evolution. Polyploidy. drift. and mass extinction all can fit into a world view of all evolution being “the accumulation of small genetic changes, guided by natural selection”.

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  • TR Gregory

    How you or I interpret what Mayr said (which differs evidently) decades after the fact is irrelevant to the issue. The point is what Gould meant then, and it is worth noting in that regard that much of the rest of the paper was spent arguing that not everything is gradual and not everything is adaptive.

    As to polyploidy, genetic drift, and mass extinction fitting into “all evolution is due to the accumulation of small genetic changes, guided by natural selection”, again we will just have to differ on that.

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  • Jonathan Badger

    Not to be overargumentative, but understanding what Mayr meant is actually more important here than what Gould meant. It’s not much of a challenge to topple a straw man version of a theory. Was Mayr actually denying that, for example, drift happens (or if it did, wasn’t evolution?)

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  • Chris Harrison

    Jonathon, how can polyploidy by described as a small genetic change? It appears to me that this phenomenon alone forces a view of evolution that is not limited to “the accumulation of small genetic changes, guided by NS”.

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  • Jonathan Badger

    Well, overexpression of p53 (which can be caused by a very small genetic change) has been shown to induce polyploidy in tumor cells. While we don’t know what exactly caused polyploidy historically in naturally polyploid species, *something* must have, and the example of p53 shows that there is no reason to suppose that it *couldn’t* have been a small genetic change.

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  • TR Gregory

    There’s a major difference between something being *caused by* a small genetic change and *being* a small genetic change. And, in any case, I would be hesitant to draw too many parallels between somatic endopolyploidy (which really just requires cytokinesis to not occur following normal replication) and polyploidy at the species level involving unreduced gametes or hybridization among species.

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  • Larry Moran

    jonathan badger said,

    Not to be overargumentative, but understanding what Mayr meant is actually more important here than what Gould meant. It’s not much of a challenge to topple a straw man version of a theory. Was Mayr actually denying that, for example, drift happens (or if it did, wasn’t evolution?)

    First, this is about what Gould said and not about Mayr. Gould has argued repeatedly that the Modern Synthesis hardened to become adaptationist by 1960. There’s very little doubt that Gould’s characterization of the Modern Synthesis is correct. In 1982, most biologist believed that natural selection was the only significant mechanism of evolution.

    But in case you’re interested, the answer to your question is “yes.” Mayr does deny that random genetic drift is evolution. That is to say, he denies it in most of his writings.

    He makes this point very clearly in One Long Argument (1991, p. 153) where he claims that drift is not evolution.

    But his view is even more obvious in his book What Evolution Is published in 2001. There is only one reference to random genetic drift in the entire book—remember, this is a book about defining evolution.

    Mayr is one of those scientists who get confused about the difference between random genetic drift and Neutral Theory. But we can take his words on Neutral Theory to be a good indication of his adaptationism. Here’s a quotation from What Evolution Is p. 199. Judge for yourself.

    Molecular genetics has found that mutations frequently occur in which the new allele produces no change in the fitness of the phenotype. Kimura (1983) has called the occurrence of such mutations neutral evolution, and other authors have referred to it as non-Darwinian evolution. Both terms are misleading. Evolution involves the fitness of individuals and populations, not of genes. When a genotype, favored by selection, carries along as hitchhikers a few newly arisen and strictly neutral alleles, it has no influence on evolution. This may be called “evolutionary noise,” but it is not evolution. However, Kimura is correct in pointing out that much of the molecular variation of the genotype is due to neutral mutations. Having no effect on the phenotype they are immune to selection.

    There you have it. If fitness isn’t involved, then it ain’t evolution.

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  • windy

    I agree that excluding drift from evolution is silly. But if Gould is talking about the situation when “Mayr’s characterization of the synthetic theory is accurate” then we need to go by Mayr’s definition that excludes drift, and the existence of genetic drift is not evidence that the synthetic theory is dead, however silly that exclusion might seem.

    And pointing to mass extinction as a special category fails to consider that catastrophic events happen on the population and species level too – if “transspecific evolution is nothing but an extrapolation and magnification of the events that take place within populations and species”!

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  • TR Gregory

    Windy — can we assume you haven’t read what Gould wrote?

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  • windy

    About what? I was simply thinking about whether two of your examples – drift and mass extinction – can be considered defeaters of the modern synthesis, given only the above definitions by Gould and Mayr.

    I should clarify a bit – Mayr is wrong if he implied that extinctions are a result of natural selection. But I don’t think it’s necessarily wrong to say that macroevolution is “extrapolation and magnification” of the events happening on the population and species level, since the latter incorporate chance events, too.

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  • TR Gregory

    Windy, it makes little sense for us to discuss Gould’s writings when you have not read them.

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  • windy

    I’ve read some of them of course, but I wasn’t talking about what Gould has written elsewhere. I was simply talking about whether polyploidy, genetic drift, and mass extinction (your list) constitute evidence against Mayr’s version of evolution. If you’re not interested in that then fine, it’s your blog, but please don’t try to twist my words around.

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  • TR Gregory

    This post was specifically about what Gould said, and moreover that he did NOT say that the modern synthesis was dead, only the strict selectionist one of Mayr. Beyond that, you’re welcome to read Gould’s writings about why mass extinction is not strictly explicable in microevolutionary ways.

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  • windy

    Beyond that, you’re welcome to read Gould’s writings about why mass extinction is not strictly explicable in microevolutionary ways.

    I’ve read such accounts, but I can’t help noticing that often these suggested “microevolutionary ways” aren’t even sufficient to explain microevolution… But I’ll butt out then since it’s outside the textual analysis of Gould.

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